Analytical Goals - PowerPoint PPT Presentation

Analytical Goals. Analytical Goals. Valid data are essential in making medical decisions , the most important concepts used in judging analytical performance :- 1)Analytical accuracy : agreement between the best estimate of a quantity and its true value

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Analytical goals should be appropriate for intended medical use, and hence will vary in different clinical situation as well as among different analytes . although one intuitively assumes that a laboratory test is usually obtained for the purpose of the

there is a basic distinction in performance requirement for two purposes , for monitoring therapy or following the course of disease the concentration of one or more substance is compared with the value obtained previously on the same patients, in this case the day to day observation must be reliable, and precision or reproducibility is the prime concern for diagnosis on other hand, the concentration of one or more substance is compared with the established reference range or discrimination values to determine if the value for the subject .

Test to determine prognosis is an extension of the diagnosis into future , accuracy are not rigid as for the initial diagnosis . for example whether the serum prostatic acid phosphatase is 5 u or 6 u /l would make little difference in predicting the course of prostatic carcinoma but equal error in activity of 1u/l could be critical in the initial detection of this tumor

Criteria for medical need in term of accuracy have seldom been define reasons are several laboratories have been in habit of defining the reference ranges believed applicable to their own local , there was little movement of patients around the country and consequently the little need for common standard for (the true value)

Since there has been less experience in comparing bias of inter laboratory results than in comparing precision , there are few published analytical goals for accuracy of clinical lab. Tests ,Gilbert in 1975 published accuracy goal as a percentage based on his experience with the evaluation of college of American pathologist CAP . survey results as shown in the table below they are stated to be approximation and to be nearly the same as coefficient of variation .

With the development of definitive method for certain analyte in serum specimens , however it has been possible to assess accuracy of performance of clinical lab. For these analytes by applying the definitive methods to serum pools used national wide survey programs .

Definitive methods usually employ isotope dilution /mass spectrometry and furnish a value that is close to two value for

the analyt in serum matrix as is obtainable with current technology , two such studies are shown in table 2, Gilbert compare the mean of the results obtained by 4200 .

CAP survey participant with definitive value for 7 analytes assigned by the US national Bureau of standard.

For urea it about 3% at extremes of the ranges of concentrated tested .

The bias in the average results of survey for many frequently assayed substance is seen to be small less than CV of the assay

this also indicate that the mean value generated in a large number of participating lab. For a common pool is a reasonable estimate of true value for these substance, this conclusion cannot applied as yet to other analyt particularly enzyme for which reaction condition vary among labs.